The present disclosure relates to heat exchangers, and in particular to closure bars for plate fin heat exchangers.
Heat exchangers are often used to transfer heat between two fluids. For example, in aircraft environmental control systems, heat exchangers may be used to transfer heat between a relatively hot air source (e.g., bleed air from a gas turbine engine) and a relatively cool air source (e.g., ram air). Some heat exchangers, often referred to as plate fin heat exchangers, include a plate fin core having multiple heat transfer sheets arranged in layers to define air passages there between. Closure bars seal alternating inlets of hot air and cool air inlet sides of the core. Accordingly, hot air and cool air are directed through alternating passages to form alternating layers of hot and cool air within the core. Heat is transferred between the hot and cool air via the heat transfer sheets that separate the layers. In addition, to facilitate heat transfer between the layers, each of the passages can include heat transfer fins, often formed of corrugated material (e.g., aluminum), that are oriented in a direction of the flow within the passage. The heat transfer fins increase turbulence and a surface area that is exposed to the airflow, thereby enhancing heat transfer between the layers.
Typically, to further facilitate heat transfer within the core, components of a plate fin heat exchanger are formed of a material, such as aluminum, that has a relatively high heat transfer coefficient. However, as hot air passes over the closure bars (e.g., closure bars at the hot air inlet), a combination of a high velocity of hot air at the inlet and a relatively high coefficient of thermal expansion of aluminum can cause rapid physical expansion of the closure bars. Accordingly, because corners of the heat exchanger restrain overall expansion of the core, such rapid expansion of the closure bars can result in physical damage to components of the core (e.g., crushing of the heat transfer fins).